Seasonic 750W for GTX SLI

Chrisn3108 · Oct 27, 2014

Hi Guys

Recently added a second MSI GTX 780 3G card in SLI but kept the same PSU which is below in the link.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817151107

I ran the system for a few hours playing BF4 on ultra on 1680X1050 22" display. Getting over 200FPS at times. Yes I know I'm on the lookout for a decent 27" 1440p.

The system was stable with the 750W but the fan got very loud, the loudest component in the case.
The PSU is SLI certified 80+bronze and comes with 4X 8+6 pin PCIE connectors so I'm thinking its good for the 780's SLI. The PSU gets only slightly warm.

Am I kidding myself here or is this thing gonna pop soon.

Thanks
Chrisn

junkeymonkey · Oct 27, 2014

http://www.nvidia.com/object/slizone_howtobuild_2.html

CraigN · Oct 27, 2014

You're not kidding yourself. an 80+ Bronze 750W PSU should be just fine, especially if it's only getting a little warm. The fan is probably just a loud fan. You could replace it with a quieter PSU, or if your case is a mid tower, get a full tower case to get better airflow/less heat ejected on top of the PSU.

Chrisn3108 · Oct 27, 2014

junkeymonkey :

Reading this article I'm assuming my rig falls in the high end category which requires +12V@30A, and the Seasonic is rated at +12V@62A. So I'm OK.

Hardware as follows:
MSI Z87 G45 mobo
i5 4670k @ 4.2Ghz
8 G Corsair LP ram
CM V8 GTS Cpu cooler
MSI GTX 780 SLI
128G SSD
1 TB WD Black
120G Seagate
DVD optical drive
CM Storm Enforcer Mid tower

Im planning to install two more Corsair 120mm AF fans for exhaust on top and see what happens ........before I decide to change the case.

junkeymonkey · Oct 27, 2014

I guess ??? why is one card require min. 750w psu but if you add another card that don't change?? so if your card pulls 30a and the psu supplies 45a your good but you add another card that requires 30a now with the 2 cards should you not be needing 60a??? so now the psu doing 45a is falling short??

and if that's so then your psu at 62a will now be puling 60a is cutting it close -0- headroom

I would think at least a solid build 850w with 70a would be better cause it not stressed for the amps its needing to supply [opinion]

junkeymonkey · Oct 27, 2014

I guess ??? why is one card require min. 750w psu but if you add another card that don't change?? so if your card pulls 30a and the psu supplies 45a your good but you add another card that requires 30a now with the 2 cards should you not be needing 60a??? so now the psu doing 45a is falling short??

and if that's so then your psu at 62a will now be puling 60a is cutting it close -0- headroom

I would think at least a solid build 850w with 70a would be better cause it not stressed for the amps its needing to supply [opinion]

Here is Guru3D's power supply recommendation:
•GeForce GTX 970 or 980 - On your average system the card requires you to have a 400~500 Watt power supply unit.
•GeForce GTX 970 or 980 in 2-way SLI - On your average system the cards require you to have an 700~800 Watt power supply unit as minimum.

If you are going to overclock your GPU or processor, then we do recommend you purchase something with some more stamina. There are many good PSUs out there, please do have a look at our many PSU reviews as we have loads of recommended PSUs for you to check out in there. What would happen if your PSU can't cope with the load:
•Bad 3D performance
•Crashing games
•Spontaneous reset or imminent shutdown of the PC
•Freezing during gameplay
•PSU overload can cause it to break down

CraigN · Oct 27, 2014

junkeymonkey :

Those are the 970 and 980, he has a 780, which has different (albeit greater) power requirements.

The GTX 780 does not require a minimum of 750W PSU. It requires a minimum of 600W.
The amp ratings on Nvidia cards are worst-case scenarios, and most of the time never pull that amperage.
The 780 is listed as requiring 42Amps. Physics will tell you 12V+ rail * 42Amps = 504 Watts. The two cards in SLI are essentially in parallel, since you have *two* connections to a single +12V rail, instead of two separate +12V rails (Some PSUs actually have this). This means that no, you don't need 30a+30a=60a to power two cards in SLI because they're not in series, circuit wise. You don't get 100% increase in performance from two cards in SLI, and they shouldn't both be running up against the wall at their max amperage ratings either, in practical performance. If they are, you've got bigger problems.

750W will hold fine, but I would recommend maybe moving up to a Seasonic 850W 80+ gold in your semi-near future. No need to burn up perfectly good graphics cards over a PSU, but Seasonic makes quality PSUs. You *should* be okay, but if you think the noise and the heat is a problem, then get a better PSU and you'll be okay. 750W is not unheard of for SLI machines, but I will agree, it is right near the ceiling. Your total system wattage is going to be just around 700W with that OC'd 4670K.

junkeymonkey · Oct 27, 2014

ya the bad thing is therews no real solid answer all I do is take what I can find as in amps and if my total amps come to 60 ig go with a psu with 70 [this includes any upgrades or oc'ing I can add in at the time ]

and like the cards this one says 500w that one says 650w this one over here claims 450w ant the one over yonder by the fence says 600w

eaven in the same line of cards the manufacture may call it different like asus don't tell you --msi says 650w gigabyte says 500w and there all the same card between the standard and oc models.

so you need to know what you want and what you may want to upgrade to in the future add it up and go higher a bit and don't go cheap on the psu's build quality

junkeymonkey · Oct 28, 2014

bottom line is if you figure you need a 750w psu you buy a 850w -- cause do you want ''good enough'' and hope or do you want something that's got it well covered and some head room to spare ???
also it can be you find the ''good enough'' down the road may not do the job and now your buying another unit when you could of just got one and been good the whole time ??

your call on what you think is best

Chrisn3108 · Nov 1, 2014

I used a wattage calculator (cant remember which one) and the requirement came up between 650 and 660W. I checked the PSU performance via AIDA64 and all is ok. But to be safe I'm gonna change it anyway. Looking at a 100W for the head room. Any suggestions on a modular silent model.

mdocod · Nov 1, 2014

Unless you replace the BIOS on your GTX780s, they won't be able to pull more than ~250-265W peak load (per card) under torture testing, and will average less than that while gaming. A pair of GTX780s can peak ~500W while being torture tested, and will average more like 350-450W while gaming.

A mildly overclocked 22nm i5 is not particularly power hungy. Depending on the characteristics of the specific chip and VRM efficiency, the peak power dissipation of the CPU and associated voltage regulation at 4.2ghz will only be ~110-120W.

The 1150 socket platform is pretty efficiant, especially with so much now integrated into the CPU (PCIE lanes, memory controller etc). The chipset's peak dissipation is only like 5-10W, that leaves RAM, Fans, Drives, Ethernet, USB devices, a few odds and ends, each of which is ~1-6W each depending..

I come up with less than 700W peak power dissipation under torture testing when I add this up. While gaming I would expect that to be closer to 500-600W averages.

Turn on Vsync and that will drop significantly until you get that 1440P monitor

CraigN · Nov 1, 2014

Most of the PSUs in the 850W range (and 80+ Gold) are fairly low-noise, Chrisn. Personally, I have a Corsair HX850, and I never even hear the fan kick up even when gaming, and it doesn't run at all when idling. Personally, I would recommend one, but I'm sure there are others who would recommend XFX, PC Power and Cooling, and Seasonic.

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